1. Field of the Invention
The present invention relates generally to workpiece templates and, more specifically, to workpiece templates used in lapping and polishing silicon wafers in either single or double sided polishing machines. The present invention is a template having a plurality of cavities within the body of the surface for inserting objects such as silicon wafers intended for lapping and polishing to a thickness equal to the depth of the template cavity.
In addition, the thickness of the intended object can be varied by inserting one or more shims into the workpiece cavity.
2. Description of the Prior Art
There are templates for lapping and polishing wafers to a desirable thickness determined by the depth of the template cavity. It has been found by the inventor that they contain one or more undesirable characteristics that render them unsuitable for repeated use.
The process of lapping and polishing wafers on a single side involves placing the workpiece or workpieces into a template and placing the template upside down between a rotating pneumatic head and a table having a controlled flow of abrasive slurry flowing onto the table surface during the pneumatic head rotation whereby the wafer blanks will be honed and polished to the thickness of the template.
There are a number of undesirable side effects that can occur in the prior art. As the wafers approach the thickness of the template cavity, the amount of fluid between the template and the lapping/polishing surface decreases causing spotted changes in the surface temperature of the template burnishing the template.
Another undesirable effect of this method relates to the cross sectional thickness of the, finished wafer. The wafers can rotate within the cavity causing the wafers to continuously butt up against the wall of the cavity and rise from the cavity base whereby the edge thickness can vary from the center thickness. This is especially undesirable in applications where tolerances are measure in microns.
An object of the present invention is to overcome these shortcomings within the prior art. The present invention also addresses another shortcoming within the prior art relating to the inordinate number of templates used because of the varied thicknesses required within the end product. The present invention addresses this need through the use of shims which can have a thickness imprinted on the shim or can be classified using a color code to indicate thickness. These shims can be permanently fixed to the workpiece cavity base having indicia indicating the thickness of the end product or a color code scheme can be used to indicate the thickness of the end product. In addition one or more shims could be removably inserted into one or more cavities to vary the thickness of the finished end product.
In addition the present invention addresses another shortcoming within the prior art related to lapping and polishing of non-standard shapes such as triangles, squares, rectangles, etc. The present invention overcomes the need for creating full sized templates for the aforementioned non-standard shapes by having smaller templates having cavities conforming to the desired non-standard shapes that are of substantially equal diameter to the cavities of the larger templates, thereby enabling lapping and/or polishing of silicon wafers of a non-standard size which also provides for the lapping and polishing of mixed wafer shapes by the selection and placements of smaller templates having the preselected shape or shapes placed within one or more cavities of the larger workpiece template.
Another additional element is provided for by the present invention in the form of channels etched into the top surface of the workpiece template for the purpose of channeling the abrasive and/or polishing fluid across the surface of the workpiece template during a lapping and/or polishing operation. Again returning to the problem of workpiece template burnishing due in some part to the lack of fluid between the workpiece template and the lapping/polishing surface, the present invention channels the lapping/polishing fluid across the entire surface of the workpiece template. Furthermore, the channels also serve to reduce hydrodynamic forces between the template and lapping/polishing operational surface caused by the rotational speed of the head, the lapping/polishing surface and the fluid therebetween by limiting the planar surface area between points of fluid transition which is currently the peripheral edge of the template.
Basically, the channels provide an abundance of fluid across the non-channeled planar surface by providing channels where fluid can be transferred from or to depending on the dynamic fluid forces at any point on the non-channeled planar surface.
Therefore, because of the aforementioned problems and shortcomings of the prior art it is felt that a need exists for the present invention and while the prior art may be suitable for the purposes for which they were designed, they would not be as suitable for the purposes of the present invention, as hereinafter described.
A primary object of the present invention is to provide a workpiece template for lapping and/or polishing silicon wafers.
Another object of the present invention is to provide a lapping/polishing workpiece template that can be repeatedly reused.
Yet another object of the present invention is to provide a lapping and polishing workpiece template having a main plate with at least one cavity therethrough for the placement of a workpiece, such as a silicon wafer, to be lapped and/or polished.
Still yet another object of the present invention is to provide a lapping/polishing workpiece template comprised of a main plate having a substantially smoothed edged circular configuration.
A further object of the present invention is to provide a lapping/polishing workpiece template having a main plate having an additional element in the form of a circumferentially notched gear-like periphery.
A yet further object of the present invention is to provide a lapping/polishing workpiece template having a main plate having a top surface and a bottom surface having a further additional element in the form of channels having a channel base and opposing channel walls placed within the top surface extending from a substantially central position to the periphery of said workpiece template.
A still yet further object of the present invention is to provide a lapping/polishing workpiece template substantially comprised of fiberglass-epoxy laminates.
Another object of the present invention is to provide a lapping/polishing workpiece template having a main plate comprising a fiberglass-epoxy laminate and having a frictionless material fixedly positioned to the bottom surface of the main plate.
Yet another object of the present invention is to provide a lapping and polishing workpiece template having a main plate comprising a fiberglass-epoxy laminate and having a Mylar backing adhesively affixed thereto.
Still yet another object of the present invention is to provide a lapping/polishing workpiece template having a main plate comprising a fiberglass-epoxy laminate and having a frictionless material fixedly positioned to the bottom surface of the main plate forming a frictionless work holder cavity base.
A further object of the present invention is to provide a lapping/polishing workpiece template having a main plate and a further additional element in the form of a backing plate being of substantially equal diameter affixed thereto.
A yet further object of the present invention is to provide a lapping/polishing workpiece template having a main plate, a backing plate with a top side and a bottom side with said top side fixedly positioned to said main plate and said bottom side having an adhesive layer.
A still yet further object of the present invention is to provide a lapping/polishing workpiece template having a main plate, a backing plate with a top side and a bottom side with said top side fixedly positioned to said main plate and said bottom side having an adhesive layer with a peelable removable covering thereon.
Another object of the present invention is to provide a lapping and polishing workpiece template having a main plate and a backing plate affixed thereto having at least one cavity positioned within said main plate.
Yet another object of the present invention is to provide a lapping/polishing workpiece template having a main plate comprising a fiberglass-epoxy laminate having a mylar backing adhesively affixed thereto whereby said mylar or other suitable frictionless material will cause the at least one wafer to rotate.
Still yet another object of the present invention is to provide a template cavity unit that will circumferentially conform to the workpiece template cavity whereby said template cavity unit can be inserted into the workpiece template cavity.
A further object of the present invention is to provide a template cavity unit having one or more cavities therein for inserting workpieces intended for lapping/polishing.
A yet further object of the present invention is to provide a plurality of shims for placement into the cavity or cavities of the workpiece template.
A still yet further of the present invention is to provide a lapping/polishing workpiece template having a shim that can be removably inserted into each of the plurality of cavities within said template.
Another object of the present invention is to provide a lapping/polishing workpiece template having a plurality of shims of varying thicknesses that can be removably inserted into each of the plurality of cavities within said template.
Yet another object of the present invention is to provide a lapping/polishing workpiece template having a shim or shims affixed to the base of the plurality of cavities within said template.
Still yet another object of the present invention is to provide a lapping/polishing workpiece template having an affixed shim or shims of smaller diameter than the diameter of the workpiece cavity diameter of the plurality of workpiece cavities within said template.
A further object of the present invention is to provide a lapping/polishing workpiece template having an affixed shim of smaller diameter than the diameter of the workpiece cavity diameter of the plurality of workpiece cavities within said template whereby the periphery of the wafer inserted therein will extend beyond the circumference of said shim.
A yet further object of the present invention is to provide a lapping/polishing workpiece template having a shim of smaller diameter than the diameter of the workpiece cavity diameter whereby the periphery of the wafer contained therein will extend beyond the circumference of said shim to reduce tapering of said wafer.
A still yet further object of the present invention is to provide a lapping/polishing workpiece template having a plurality of shims manufactured from a suitable material such as polyurethane.
Another object of the present invention is to provide a lapping and polishing workpiece template having a plurality of shims color coded for various thicknesses that can be removably inserted into each of the plurality of cavities within said template whereby said template can be used to produce wafers of various thicknesses.
Yet another object of the present invention is to provide a lapping and polishing workpiece template wherein a plurality of color coded shims representative of various thicknesses can be inserted into one or more of the workpiece cavities to produce wafers of a calculated thickness equal to the total workpiece template cavity thickness minus the total of the shim or shims inserted therein.
Additional objects of the present invention will appear as the description proceeds.
The present invention overcomes the shortcomings of the prior art by providing a method and device whereby employing the reusable workpiece template and selectively inserting shims having means for identifying various thicknesses, will produce semiconductor wafers of varying thicknesses.
In addition, the workpiece template having one or more cavities with a shim centrally positioned therein and being of smaller diameter than the cavity base will reduce tapering of the wafer. Additionally, the shims manufactured from a suitable frictionless material, such as mylar, will induce rotation of the wafer further reducing tapering of said wafers.
Furthermore the workpiece template having channels formed therein provides means for the lapping/polishing material to circulate across the planar surface of the workpiece template eliminating burnishing of the template and unwanted hydrodynamic properties of the lapping/polishing material associated with a fluid compressed between the two planar surfaces of the workpiece template and the lapping/polishing surface.
The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying drawing, which forms a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. In the accompanying drawing, like reference characters designate the same or similar parts throughout the several views.
The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.
10 workpiece holder
12 lapping/polishing machine
14 lapping/polishing surface
16 supply of abrasive material
18 abrasive material
20 rotating heads
22 main plate
24 main plate cavity
26 top surface of main plate
28 bottom surface of main plate
30 main plate exterior wall
32 workpiece template cavity wall
34 workpiece template cavity base
36 frictionless material
38 adhesive layer
40 removable protective layer
42 gear-like notches
44 workpiece surface channel
46 channel base
48 channel wall
50 backing plate
52 backing plate top surface
54 backing plate bottom surface
56 template cavity unit
58 template cavity unit exterior wall
60 template cavity unit top surface
62 template cavity unit bottom surface
64 template cavity unit cavity
66 shim